Electroforming method of making molds



Oct. 7, 1941.

A. C. DUNN ELECTROFORMING METHOD OF MAKING MOLDS 4 Sheets-Sheet 1 Filed Nov. 20, 1936 INVENTOR ANDREW C. Du/v/v I #IATTQRNEYS.

Oct. 7, 1941. A. c. l DUNN 2,258,579

ELECTROFORMING METHOD OF MAKING MOLDS Filed Nov. 20, 1936 4 Sheets-Sheet 2 INVENTOR. AN REW C. DUN/v airrolmms.

Oct. 7, 1941.

A. C. DUNN TZ-IOD OF MAKING MOLDS ELECTROFORMING ME Filed Nov. 20, 1936 4 Sheets-Sheet 3 INVENTOR. ANDREW C. Du/v/v ATTORNEYS Oct. Z, 1941. 'A. c. DUNN ELECTROFORMING METHOD OF MAKING MOLDS 4 Sheets-Sheet 4 Filed NOV. 20, 1936 IINVENTOR. BY ANDREI v C. D NN /%c a a ATTORNEYS Patented Oct. 7, 1941 UNITED- STATES PATENT OFFICE ELECTBOFOBMING METHOD OF MAKING MOLDS 7 Andrew G. Dunn. Chlcagmlll. Application November 2c, 1936, Serial No..ll1.869

scams. (cuts-s) This invention relatestomolds'. to be used as patterns for casting in under the like or for direct molding of plastic'material such as rubber and to the method of making such molds.

One of the objects of the invention is to pro- 'vide a novel method of making molds in which substantially all hand work is eliminated and in which an extremely accurate mold may be formed quickly and easily. This is preferably accomplished by shaping wax to conform to the article to be made and electroplating over the wax. The electroplate, suitably reinforced, forms A shrinkage to distort the electroplate. Instead of so wax I8 is poured thereover to fill the frame l1.

plaster, rubber or the like may be used if desired,

the low temperature at which it is cured being in-' sufllcient to warp or shrink the electroplate.

Other objects and advantages of the invention relate to the novel molds and to various other novel features of the method of making them as 25 will appear more fully from the following description when read in connection with the accompanying drawings. in which:

Figure 1 is a perspective view of an article to be cast:

Figures 2 and 3 are perspective views of core members;

Figure 4 is a section through a wax-mold;

Figureb is a plan view of a'molding frame; Figure 6 is a bottom viewof the frame-of ins e 5:

Figure 7- is a cross-section similar to Figure 4 illustrating a step in one method of forming a matchplate according to the invention:

Figures 8 and 9 are sections illustrating further j steps in the making of ma'tchplates;

Figures 10 and 11 are perspective views of a completed'matchplatm' "top It having a plurality of screw holes llthereinand carried by a curving base portion l2. It will be understood that this article has been sethe invention imequallyapplicable to articles of substantially any size or shape. a

A core member I! shown in Figure 2 is shaped from any. desired material to fit the lower side 5' of the bracket and is formed with a tapered portion ll to project out the open side of the I bracket. A similar core member it, Figure 3,

is provided to form a gate. In'carrying out the novel method the bracket 10 is placed over the core member i2 and both are laid on a flat plate I, preferably of glass or the like. The core-member I! is placed in a positiorr abutting the bracket and a frame I! is laid on the plate IS. The exposed surfaces of the 15 plate. the bracket and the core members are then coated with a parting material which may be the parting solution more particularly described .and claimed in my copending application Serial No. 111,870, flied November 20, 1936, and molten Preferably dowel pins I! are placed in the wax to form guide openings for a purpose to appear later; A

After the wax It has hardened, which operasired, it is removed from the frame l1 and from the bracket and core members. Thus there is formed a block of wax "it having one surface 7 a impressed to conform to one side of the bracket "I. As shown herein six such blocks it are formed although any desirable number could be made and used as will be apparent. A

The six blocks II are laid on a flat plate of glass or the like 2| with their impressed sides down and an 'opentop frame 22 islaid on the plate 2| around the blocks. A runner .23 of copper or the like is laid on the plate between the blocks it which butt up against the runner so that it will serve to close the openings formed by th core members ll With all of the parts in place as described, molten wax is poured into the frame 22' to bind together the blocks It and the runner .23 in one large block of wax as shown 1 a at2linFigure8.

According to one novel method, the impres-- sions of the gates II in'the wax block 24 as shown at 25 in Figure 6 are filled with some suitable material such as soft plaster and the hollow so runner 23 is similarly filled to present a smooth A plurality of replicas of the bracketsurface. to be cast are then placed lnthe impressions l8 and the whole exposed surface is coated with parting solution'. These replicas may be metal lected purely for illustrative purposes and that 66 duplicates of the pattern bracket or may be wax .tion may be speeded up by refrigeration if de- A or plaster replicas thereof formed in any suitable manner. a

- A frame 28 is then placed on the frame 22,

dowel pins 21 serving to aline the frames, and molten wax 28 is poured into the frame 25. Thus the wax block 28 receives a series of impressions of the lower side of the bracket I 8 exactly matching the impressions of the upper side formed in the block 24. After the wax 28 has hardened the wax blocks 24 and 28 are separated, the plaster is removed from the gate impressions l and runner 23 in block 24 and the impressed surfaces of both blocks are electroplated in any well known manner to form electroplates 29 and 30 as shown in Figure 9.

After the electroplating is completed, the

frames 22 and 28 are arranged face to face as shown in Figure 9 with suitable spacers 3| holding them in spaced relationship and the space 32 between the electroplates is filled with plaster.

When the plaster sets, the edges of the electroplates are trimmed off and are preferably soldered together to form the completed matchplate shown in Figures and 11. It will be noted that in these figures the electroplates 29 and are joined together and are reinforced by plaster 33, the plaster itself being further reinforced by the use of wire screening or the like, not shown, to increase-its strength.

According to a variation of the method. described above, the blocks 24 and 28 may be separated by spacers prior to electroplating and the space between them may be filled with plaster. After the plaster has set the blocks 24 and 28 may be removed and the surface of the plaster electroplated to provide it with a hard, smooth sur-- face. When this procedure is followed, the electroplate is preferably made very thin and serves primarily to form a hard, smooth surface on the plaster.

Figure! illustrates one step in an alternative, and perhaps preferable, method of forming the matchplate in which the plate It and the core l3 are removed from the block l8 as shown in Figure 3, leaving the bracket l0 and gate core l5 in place therein. The exposed surfaces are coated with parting material and a frame 34 is l8 by means of the dowel pins and are covered with wat: to form a single wax block similar to the block 28. Thereafter the remainder of the process is the same as that described above to form the completed matchplates.

With both processes it will be noted that the metal runner 23 is left in place and that the plating will adhere thereto so that it forms a substantially integral part of the electroplate 29. It will also be noted that a very accurate matchplate will bequickly and easily formed with substantially no hand work. The process as last described permits any number of matchplates or molds to be made with a single pattern without the necessity for making wax'or other replicas thereof and also eliminates the necessity for filling the impressions of the gate cores with plaster or the like in forming the second wax block as in the case of the first described process.

Figures 12 to 14 illustrate an alternative method of forming a plate similar to the plate 29 which is particularly useful when a number of metal patterns or replicas of the article to be cast are available. According to this method a number of the replicas 38 arelaid on a plate of glass or the like 31 with a metal runner 38 connected thereto by metal gates 39. A frame 40 is then placed on the plate and filled with molten wax 4| to bind the replicas, gates and runner together.

Thereafter the plate 31 is removed and the exposed surface is plated to form an electroplate 42 which adheres to and rigidly connects the replicas ceive impressions of the articles to be molded, I have found that plaster can be used equally well cured by heat.

'and in some cases is preferable since it is subjected to less shrinkage upon setting than wax.

I have also found that with plaster it is not necessary to coat the pattern with parting solution, particularly if it is clean, but where plaster contacts plaster as in pouring the bottom half of the mold parting solutiorris essential.

When plaster is used it is made up into a thin solution which is 'poured in exactly the same manner as the wax described above and is allowed to set, the setting action being speeded up if desired by the use of a drying oven. After the plaster has set the impressed surface is washed to remove any remaining partingsolution and is thinly coated with varnish or'lacquer which is preferably sprayed on. The varnish is allowed to dry to a tacky state and is then rubbed with molding lead or lampblack and polished by brushing with graphite to form a conducting surface for electroplating.

-Various materials other than wax or plaster which can be poured in liquid form might be employed in lieu thereof, and it is intended that the term "plastic material" as employed in this specification and .claims shall include all such materials.

Figures 15 and 16 illustrate the application of the invention to the manufacture of molds for plastic material, core boxes, core dryers and the like. For this purpose wax replicas 43 of the article to be molded are made, each replica simulating only one side of. the article to a suitable parting line. These replicas are secured to a plate 44 of wax or the like and the plate and replicas are electroplated as indicated at 45. Where the molds are to be used for rubber or other plastic material a strip of ,wax 46 is preferably laid around each replica to'form a cavity to receive excess material. 'A frame 41 is placed on the electroplate and is filled with plaster 48 to form a reinforcingbody. Since plaster is a rather poor heat conductor, metal filings or wires are preferably mixed therewith when the molds are to be used for rubber or other material which is Afterthe plaster 48 has hardened the wax is removed and, if desired, the electroplate 45 may be replated with chromium to provide a hard smooth surface. It willbe understood that pairs of mating molds are formed as shown in Figure 18- glhich may be used in place of the usual molding Instead of using plaster to reinforce the electroplates, other material which may be applied and caused to harden without excessive heat may be employed. Thus raw rubber could be applied to the electroplates and cured in place, the relatively low temperature required to cure the rubber not being suflicient to cause warping or shrinking of the electroplates.

While several embodiments of the invention have been shown and described in detail, it is not intended to limit the scope of the invention thereto or otherwise than by the terms of the appended claims.

I claim: I 1. The method of making molds comprising placing a plurality of molds on a plate, pouring plastic material over said molds to bind them tothe blocks together, placingreplicas of said artigether, removing the plate, electroplating the sur-' face of said molds and said material to, form a single electroplate, reinforcing said electroplate with plaster, and removing the plastic material,

2. The method ofmaking matchplates com-- prising forming a plurality of impressions of one side of an article to be cast in a block of plastic material, placing replicas of said article in the impressions, coating the exposed surfaces of said replicas and said block with parting material, pouring plastic material over said exposed surfaces, to farm a second block having matching impressions of the other side of the article, eleccle in the impressions, coating the exposed surfaces of the replicas and the block with parting material, pouring plastic material over said exposed surfaces to form a second block having matching impressions of the other side of the article, electroplating the exposed surfaces of the blocks. and connecting the electroplates.

4. The method of making matchplates comprising forming a plurality of blocks of plastic material with impressions of .one side of an article to be cast, placing said blocks on a plate, placing a metallic runner on the plate adjacent the blocks, pouring plastic material over the blocks and runner to bind them together, electroplating over the runner and the impressed surfaces'of the blocks to form a singe electroplate integrally bonded to the runner and shaped to conform with the impressed surfaces of the blocks, forming a second block having matching impressionsof the other side of the article, electroplating said sec- 0nd block, and securing the electroplates together.

ANDREW C. DUNN. 

